910 FXUS66 KPQR 251717 AFDPQR Area Forecast Discussion National Weather Service Portland OR 918 AM PST Sat Feb 25 2017 .SYNOPSIS...An upper ridge will move from north to south across the area today for a brief break in rain and some sunshine. A low will then approach from the north this evening. A cold front will produce rain and mountain snow late tonight through Sunday. Snow levels will be around 1500 feet so the coast range and Cascade foothills should have accumulating snow. A couple of weak lows will continue showers Sunday night through Wednesday. && .SHORT TERM...Today through Tuesday...An east west oriented ridge of hgh pres was seen in water vapor pictures shifting south along the WA coast this morning, between two shortwave troughs in a northerly flow. A high stratocumulus deck seen over the interior of sw WA extending south down to around Mt Hood was indicative of some residual low level moisture that may wind up resulting in some cumulus today. Otherwise there were also some areas of low clouds and fog mainly in the interior valleys that was generally pretty fragmented, and should break up by afternoon. Remainder of short term discussion unchanged...Another upper level shortwave and associated surface low will drop down from the B.C. coast tonight and produce another round of rain and snow for SW Washington and NW Oregon. Precipitation will spread from north to south with a cold front late tonight through Sunday afternoon. Snow levels will be between 1000 and 1500 feet, but would not be surprised if snow occasionally mixes down to elevations slightly below 1000 feet. Modeled 850mb temperatures are a couple degrees warmer than it was for the last few lows, and do not think there will be snow down to near the valley floors. Expect the coast range, and the Cascade foothills to get 3 to 5 inches of snow from late tonight through Sunday afternoon, with 4 to 8 inches for the Cascades, and have issued winter weather advisories for these locations. The interior valleys can expect 0.25 to 0.5 inch of rain, and 0.5 to 0.75 inch of rain is possible for the coast. Rain and snow showers behind the front will persist Sunday night and Monday as the low moves inland across NW Oregon, with little change to the snow levels. A weak upper level trough will slide north to south Monday night and Tuesday for continued showers and seasonally cool weather. ~TJ .LONG TERM...Tuesday night through Friday...Showers will decrease south of Salem Tuesday night and Wednesday as high pressure begins to build over the area and moves the storm track further north. Showers will likely continue across extreme north Oregon and SW Washington. The upper ridge will intensify Wednesday night as a low over the Gulf of Alaska digs south into the NE Pacific for a brief break in precipitation Wednesday night and Thursday. A warm front will bring rain to extreme NW Oregon and SW Washington Thursday night before a cold front produces more widespread precipitation Friday. Snow levels are expected to rise to around 3500 to 4000 feet by Friday. ~TJ && .AVIATION...With weak high pres and light winds over the region this morning, IFR fog and low stratus has formed over most of the lowlands. The exceptions are at KONP at KTTD, where light offshore flow has kept conditions clear. The low cloud layer is very thin and should burn off fairly quickly later this morning. Then expect VFR conditions this afternoon and evening. Another low pres system approaching from the north with bring increasing rain and likely MVFR conditions overnight into Sun morning. KPDX AND APPROACHES...Expect IFR stratus to burn off between 18Z-19Z. Then VFR conditions prevail this afternoon and evening. Rain and MVFR cigs spread back in overnight into Sun morning. Pyle && .MARINE...Light offshore flow with seas 5 to 7 ft early this morning will persist through most of today. Next low pressure system from the Gulf of Alaska will arrive tonight into Sun as a surface low tracks south down the Pacific NW shoreline. Will see winds increase over the waters as the low tracks along the coastline. Have issued Small Craft Advisories for Winds and Seas as swell will also increase behind the low. Beyond Sunday, a lack of organized surface low pressure centers will limit chances for small craft strength winds until much later in the week. Seas will follow this same pattern, approaching near 10 feet on Sunday/Sunday night and again later in the week ahead of the next front. Pyle/Bowen && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory from 1 AM to 7 PM PST Sunday for Northern Oregon Cascades. Winter Weather Advisory from 1 AM to 4 PM PST Sunday for Coast Range of Northwest Oregon-Northern Oregon Cascade Foothills. Winter Weather Advisory from 4 AM to 7 PM PST Sunday for Cascade Foothills in Lane County-Cascades in Lane County- Central Coast Range of Western Oregon. WA...Winter Weather Advisory from 1 AM to 7 PM PST Sunday for South Washington Cascades. Winter Weather Advisory from 1 AM to 4 PM PST Sunday for South Washington Cascade Foothills-Willapa Hills. PZ...Small Craft Advisory for winds from 10 PM this evening to 4 PM PST Sunday for Coastal Waters from Cape Shoalwater WA to Cascade Head OR out 60 nm. Small Craft Advisory for hazardous seas from 4 AM Sunday to 4 AM PST Monday for Coastal Waters from Cape Shoalwater WA to Florence OR out 60 nm. Small Craft Advisory for winds from 1 AM to 4 PM PST Sunday for Coastal Waters from Cascade Head OR to Florence OR out 60 nm. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. The area is commonly referred to as the forecast area.
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